Recently, as mobile communication devices such as a smart phone are increasingly sophisticated with multi-functionality, it is required that passive elements including a substrate are densified, further sophisticated, and miniaturized as well as active elements such as a semiconductor element are highly integrated and densified. The multilayer glass ceramic substrate is used in bare chip mounting multi-chip module, mobile communication module, and on-vehicle ECU substrate. However, by incorporating passive elements such as a capacitor, an inductor, and a resistor in the inside, it enables to reduce a mounting area and thereby it enables to advance miniaturization and high functionalization.
For example, when a resistor element is formed on the substrate, desired resistance value can be adjusted by measuring an initial resistance value and then performing a laser trimming and the like, after resistor pastes are printed and then fired. However, when the resistor element is formed inside the multilayer glass ceramic substrate, a laser trimming and the like cannot be performed and it is unable to adjust the resistance value of resistor. Therefore, it becomes important to control fluctuation of resistance value in the processes of printing and firing and the like.
Further, for the method of forming a resistor inside the multilayer glass ceramic substrate, the following methods are known, for example. By respectively adding solvent, organic binder, dispersing agent, plasticizer and the like to ceramic powders and then blending, ceramic slurry is produced. The ceramic slurry is applied on a support body such as a PET film and the like to form a ceramic sheet called a green sheet. On this green sheet, conductor pastes such as silver and resistor pastes are printed. By laminating a plurality of the above sheets and firing after performing thermocompression, it enables to obtain a multilayer glass ceramic substrate wherein a resistor is incorporated.
For example, in Japanese Published Application No. 2006-108530, the resistor paste is made by blending conductive powders and glass powders. By using the resistor paste that a transition temperature Tg of glass component included in the aforementioned glass powders and a firing temperature Tc of ceramics satisfy the relation “Tc−150≦Tg≦Tc”, it enables to inhibit a dispersion of the glass component in the resistor into the glass ceramic and thereby enables to obtain a resistor-incorporated multilayer glass ceramic substrate that the fluctuation of resistance values among products is improved.
Further, the resistor is subject to stress in a shrinkage direction from the outside to the inside, which is caused by shrinkage due to a sintering of ceramics. Therefore, even if the glass does not reach a softening point, it enables to transform the glass from a powdered state into a sintered state by receiving the stress from ceramics if a glass transition occurs. In view of the above, the range is specified by the firing temperature Tc and the transition temperature Tg of glass component of resistor paste.